Thermogenic, thermolytic and body temperature effects of fenfluramine, a 5-hydroxytryptamine agonist, in the domestic fowl ( Gallus domesticus)

Abstract

1. 1. Intramuscular injection of the 5-HT agonist dl-fenfluramine increased the metabolic rate of mature cockerels by about 25% over the following 22 hr. The acute effect, over the 3 hr following injection, attained 40% at 10°C, 35% at 20°C and 25% at 32°C. 2. 2. Heat loss mechanisms (peripheral vasodilatation, postural change and panting) were also stimulated, to an extent which varied with ambient temperature. 3. 3. Food intake, respiratory quotient and locomotor activity were significantly reduced by fenfluramine injection. 4. 4. The opposing effects on heat production and heat loss had an influence on deep-body temperature which varied from a reduction of 0.5°C at 10°C ambient to an increase of about 0.5°C at 32°C. 5. 5. The 5-HT blocker, methysergide, prevented the effects of fenfluramine on both heat production and heat loss for about 5 hr after injection. 6. 6. The autonomic ganglion blocker, hexamethonium chloride, reduced the thermogenic but not the heat-loss effects of fenfluramine. 7. 7. The results suggest that dl-fenfluramine has centrally-occurring but independent effects on heat production and a number of heat loss effectors, and that the heat production effect is mediated by the autonomic nervous system. The effect of fenfluramine on deep-body temperature appears to result from an altered equilibrium between heat production and heat loss.